Field
The disclosed technology generally relates to semiconductor fabrication, and more particularly to plasma etching.
Description of the Related Technology
When a porous substrate needs to be treated by etching, damage of the substrate often occurs. This is particularly true with plasma mediated treatments. This is presumably caused by active plasma radicals penetrating deeply into the porous substrate and reacting therewith, thereby changing its composition and its porosity. Both oxidative and reductive plasmas have such detrimental effects. These problems for instance occur in the field of microelectronics during integration of low-k dielectrics.
Low-k dielectrics, understood in semiconductor processing as referring to dielectric materials having a dielectric constant lower than the dielectric constant of SiO2, i.e. lower than 4.0, are often used to decrease capacitance between nearby conductive portions of high density integrated circuits and thereby avoiding loss of speed (e.g., due to RC delay) and cross-talk (e.g., through capacitive coupling of adjacent conductive lines). In order to decrease the dielectric constant of low-k dielectrics as much as possible, low-k dielectrics are made porous. Thereby, the dielectric constant can be lowered down to about 2.0 or even less. Integrated circuit fabrication processes on dielectrics involve plasma etching and expose therefore the dielectrics to the damage mentioned above.
EP2595182 discloses, among other things, a method for treating a surface of a porous material in an environment, the method comprising the steps of:                I. Setting the temperature of the surface to a value T2 and setting the pressure of the environment to a value P1,        II. Contacting the surface with a fluid having a solidifying temperature at the pressure value P1 above the value T2 and having a vaporizing temperature at the pressure value P1 below 80° C., thereby solidifying the fluid in pores of the material, thereby sealing the pores,        III. Treating the surface, wherein the treatment is preferably an etching or a modification of the surface,        IV. Setting the temperature of the surface to a value T3 and setting the pressure of the environment to a value P2 in such a way as to vaporize the fluid.        
Although this method can be effective at preventing some damage to porous substrates, an undesirable amount of damage can still occur.
There is therefore a need in the art for a way to further prevent damage to porous substrates upon treatment of the substrate (e.g., via etching or surface modification).